This was my first attempt at building a server. I spent about 3 days researching compatibility of components and software. My goal was to get the best bang for my buck. The entire server was built around the Intel Xeon 5520 processors. I chose them because they were cheapest Quad-Core Nehalem Xeon processors with HyperThreading. ESXi sees 16 logical processors with 2 of these installed! All of the hardware is on the HCL for ESX 4.0. I bought all of the components except for the redundant power supply from Newegg.com. At first I tried to save money by not buying a hardware RAID controller or an optical drive. I was able to plug a regular desktop SATA DVDRW drive into the motherboard and run the cable out of the back. I used an old power supply to power it up. It worked just fine. However, when I tried to use the onboard software RAID, ESXi was having none of that. I tried everything to get it to work. I even let the whole array initialize for 2 days! Long story short, ESXi doesn't work with software RAIDs. I decided that I shouldn't skimp on the RAID controller and ended up buying a fairly high-end one. I also bought a slim DVD drive so my server didn't look so rigged up. After I put everything together and started to install ESXi 4.0, it couldn't find the RAID! Come to find out, you have to install the RAID controller in the x16 (shaped) slot for ESXi to find it. There were 3 PCI-Express slots on the motherboard, 1 that looked like an x16 and 2 that looked like x8's. They were all x8's though. Overall it took me about 2 weeks to get everything together and working (and about 2 bottles of Xanax... just kidding).I ended up saving quite a bit of money over comparably spec'd name-brand servers.

Chassis: Intel SR2600URBRP 2U Rackmountable $1300

Motherboard: Intel S5520UR included with chassis

Processors: 2 x Intel Xeon 5520 $756

RAM: 12 x Crucial DDR2 1333 2 GB Unbuffered ECC (24 GB total) $432

RAID Controller: Adaptec 5805 SATA/SAS Kit $590

HDD: 4 x Western Digital RE3 1TB SATA $640

Optical Drive: LITE-ON Slim SATA 8x DVD burner $40

Redundant Power Supply: Intel AXX750WPS from Buy.com $198

Total Cost: $3956 without shipping

This configuration runs flawlessly with ESXi 4.0 free license.

Using RAID 10 or 1+0, ESXi has 1.81 TB available for the datastore.

I have 5 XP VMs, 3 Ubuntu 9.04 web servers, and 2 Windows 2k Servers running simultaneously. This has put no noticeable load on the server. Average CPU usage under a heavy load is 325 MHz! Average RAM usage is 544 MB!

that's quite a nice machine you have there. Have you measured its power consumtion, for example in a completely 'idle' state (no VMs running) and in a production state (with all your VM up and running)?

I am currently build a very similar machine for my company as a lower cost lab machine.

I have done about 3 days of research to make sure everything is compatible but now I found what could be a major issue. In one of the Adaptec RAID 5805 'read me' documents it states:

"Upgrading the VMware driver to ESX 4.0 is currently supported only for non-bootable arrays. For Bootable arrays, upgrading will result with booting only to an ESX recovery shell with no option to reboot to ESX server normally."

I noticed you have nearly the same system... Are you booting from your array handled by the 5805? Or are you using a separate boot device for ESXi??